On Aquatic Carnivorous Coleoptera or Dytiscida. 839 
middle of the prosternum shows no perpendicular face in front in the middle ; the 
pectoral prominence is very coarsely sculptured while the adjacent lateral parts are 
smooth; the suture between the hind coxa and metasternum approaches near to the 
middle coxa; the coxal processes are highly developed and greatly prolonged be- 
hind, the prolonged angles being rendered sharply acuminate by bearing some rigid 
ciliz; the swimming legs are rather slender, the femora and tibize but little flattened 
or laminate; the former bear a well developed group of cilize at the extremity of 
their hind margin; the tarsi are about as long as the tibize, their basal joint as long 
as, or longer than, the three following ones together. 
This genus has been mixed with Hydrocanthus, but was separated by Crotch so 
far as regards the North American species; he suggested for it the name of Suphisellus, 
but not in a formal manner—only as it were hypothetically, and I have thought it 
on the whole better to use a new name. 
It is very distinct from Hydrocanthus, by the small size, the oreatly narrower 
prosternal process, and the feeble swimming legs. 
The species seem to be found in the warmer parts of both hemispheres, but so far 
as yet known are absent from Australia. 
I. 10.—Genus HYDROCANTHUS. (Vide p. 279.) 
This aggregate consists of about twelve species; they are the most highly 
organised of the Noterides, the size varies between 4 and 8 m.m. of length, the form 
is somewhat elongate, very acuminate behind, very convex transversely above, the 
surface is extremely polished, and is never variegate by spots or stripes. The 
antenne are slender, and are rather short, the middle joints of the antenne: often 
distinctly a little longer than the others, but scarcely broader. The terminal joint 
of the labial palpus is excessively dilated, but a notch or emargination can scarcely 
be detected on it. The front coxee are rather broadly separated, and the prosternal 
process behind then becomes extremely broad, so that it is frequently much broader 
than long, it is nearly truncate behind, and its angles are either rectangular or 
acute; the front band of the prosternum is rather large, and does not present any 
perpendicular face in the middle ; the pectoral prominence is very highly developed, 
so that there is formed as it were a continuous prominent platform extending along 
the middle of the body from the front coxz to the hind legs, and becoming broader 
as it extends backwards; this prominence is more or less punctate, while the 
adjacent parts are smooth ; the suture between the metasternum and hind coxa, does 
not approach very near to the middle coxa ; the coxal processes are highly developed, 
and greatly prolonged behind, the prolonged angles being rendered acute by a group 
of rigid ciliz: the swimming legs are highly developed, the femora and tibize being 
much inerassate and flattened, the former are traversed along the middle of their 
lower face with a series of punctures parallel with the hind margin, and are 
furnished at the extremity of their hind margin with an extremely highly developed 
